create requisite output directories for build targets; refactor common buile functionality into Builder#standard_build()

lib/rscons/builders/library.rb

@@ -21,12 +21,7 @@ module Rscons
           'SOURCES' => objects,
         })
         command = env.build_command(env['ARCOM'], vars)
-        unless cache.up_to_date?(target, command, objects)
-          FileUtils.rm_f(target)
-          return false unless env.execute("AR #{target}", command)
-          cache.register_build(target, command, objects)
-        end
-        target
+        standard_build("AR #{target}", target, command, objects, env, cache)
       end
     end
   end

lib/rscons/builders/object.rb

@@ -55,6 +55,8 @@ module Rscons
                    end
       command = env.build_command(env["#{com_prefix}COM"], vars)
       unless cache.up_to_date?(target, command, sources)
+        FileUtils.mkdir_p(File.dirname(target))
+        FileUtils.rm_f(target)
         return false unless env.execute("#{com_prefix} #{target}", command)
         deps = sources
         if File.exists?(vars['DEPFILE'])

lib/rscons/builders/program.rb

@@ -28,11 +28,7 @@ module Rscons
           'LD' => env['LD'] || ld_alt,
         })
         command = env.build_command(env['LDCOM'], vars)
-        unless cache.up_to_date?(target, command, objects)
-          return false unless env.execute("LD #{target}", command)
-          cache.register_build(target, command, objects)
-        end
-        target
+        standard_build("LD #{target}", target, command, objects, env, cache)
       end
     end
   end